This application claims benefit of Japanese Patent Application No. 2004-267556 filed on Sep. 14, 2004, the contents of which are incorporated by the reference.
The present invention relates to portable terminal set and portable terminal control method capable of suitably receiving data of a service for broadcasting data of a large volume of contents including video and images to a plurality of portable terminal sets.
As a mobile communication system, a service is provided, which broadcasts data of a large volume of the same contents including voice and images to a plurality of portable terminal sets. This system is called MBMS (Multimedia Broadcast Multicast System).
In MBMS of broadcast type, a number of portable terminals receive a common channel (hereinafter referred to a common channel). Therefore, it is impossible to control power of the common channel based on the receiving quality of each portable terminal. This means that it is impossible to control the receiving operation for each data broadcast via the common channel. For example, in the neighborhood of the boundary between the coverage areas of base stations, in which the received signal quality is subject to deterioration, the portable terminal receives the same data from a plurality of base stations at different timings spaced apart by a predetermined time interval, decodes the signal from each base station, and selects data of good or better quality (this method being hereinafter referred to as selective combining method).
For example, even in the case of failure of normal reception and decoding of data transmitted from one base station, if data transmitted from a different base station later could be normally received and decoded, it is possible to select the defect-free data. It is thus possible to improve the received signal quality in the base station coverage area boundary neighborhood.
Literate 1 (Japanese Patent Laid-open 2000-115070) proposes a one-time broadcast system, in which at the time of one-time broadcast one-time broadcast discrimination data for discriminating the one-time broadcast is transmitted to and stored in the receiving set side, at the time of one-time broadcast start the receiving set receives one-time broadcast data discrimination data from a relay means, compares the received data with already stored one-time broadcast discrimination data and, when the two data are identical, limits the reception. The system thus can present reception of the same one-time data in the receiving set a plurality of times.
Literature 2 (Japanese Patent Laid-open 2001-103529) proposes a communication terminal set, in which at the time of soft hand-over for communication with a plurality of base stations the quality of down line signals from the plurality of base stations is checked, and a base station of good down line signal quality is selected to be the next transmitting station in selective synthesis unit. It is thus possible to obtain high quality reception.
Literature 3 (Japanese Patent Laid-open Hei 11-284635) proposes an ATM cell transfer control method and transfer control system, which is effective in the case of burst cell defect generation during data transfer with AAL5 due to failure in a re-transfer process in a layer upper than a CPCS layer of the AAL 5 as a result of transfer quality deterioration or reception level deterioration caused by fading in a wireless transmission section. In such case, introduction of unnecessary traffic in a subsequent stage ATM backbone network can be prevented by stopping the transmission of cell data subsequent to the defect cell providing cell number data of cells before the defect cell to cell data. Besides, the unnecessary traffic part can be made charge-free in the ATM backbone network to improve the efficiency in use of the ATM backbone network.
The above prior art inventions, however, have the following problems.
The selective combining method for data broadcast by MBMS, even when earlier data transmitted from a certain base station has been suitably received and decoded, the same data later transmitted from a different base station is received and decoded, and RLC (Radio Link Control) as an upper rank layer checks whether the same data is already present and discards data determined to be the same. Therefore, consequently data receiving/decoding process on the same data is executed a plurality of times.
According to the invention disclosed in Literature 1, at the time of the one-time broadcast start the one-time broadcast discrimination data is received from the relay means and compared with the already stored one-time broadcast discrimination data, and when the two compared data are identical, the reception is limited, thereby preventing the reception of the same one-time broadcast by the receiving set a plurality of times. However, irrespective of whether the data transmitted earlier has been normally received, the reception of the data transmitted later is rejected. Therefore, data quality reduction is liable.
According to the invention disclosed in Literature 2, at the time of soft hand-over for communication with a plurality of base stations, the quality of the down-line signals from the plurality of base stations is checked, and a base station with good down-line signal quality is selected to be the next transmitting station in the selective synthesis unit. It is thus possible to receive good quality line signals. However, receiving/decoding process is executed on the same data a plurality of times.
According to the invention disclosed in Literature 3, in the case of detection of a defect in the received data, the reception of data subsequent to the defect detection is stopped, thus preventing unnecessary data reception and improving the network use efficiency. However, it is impossible to receive normal data.